Triphenylmethylphosphonium (TPMP+) as a probe for peritubular membrane potential in the kidney slice.

The present work was undertaken to assess the validity of the use of TPMP+, a lipophilic cation, as a basolateral membrane-potential probe in the rabbit kidney slice. Cortical slices incubated in media containing 3H-TPMP+ reached an equilibrium slice/medium concentration ratio (S/M) for TPMP+ after 90 min. The equilibrium S/M TPMP+ was approximately 20 at TPMP+ concentrations between 30 and 50 microM. Concentrations of TPMP+ above 50 microM resulted in changes in tissue electrolytes and O2 consumption. Anaerobic incubation of slices in the presence of iodoacetamide decreased the S/M TPMP to approximately 3. When medium K+ was progressively increased, the S/M TPMP+ decreased continuously. There was a linear correlation between cell water/medium concentration ratios (C/M) for TPMP+ and K+ (r = 0.629, P less than 0.01). However, the C/M TPMP+ was 29.0 even at C/M K+ of 1.0, strongly suggesting the presence of a tissue binding component for TPMP+. When corrections are made for the above binding, the average C/M TPMP+ in slices incubated in the normal medium was approximately 13, equivalent to a Nernst potential of -64 mV. This value compared favorably to -54.3 mV obtained by microelectrodes in slices treated in the same fashion. It is concluded that the C/M TPMP+ corrected for binding may be used as a measure of the basolateral membrane potential in the steady state.